interface A {
    double f(double x,double y);
}
class B implements A {
   public double f(double x,double y) {
     return x*y;
   }
   int g(int a,int b) {
        return a+b;
   }
}
public class E {
public static void main(String args[]) {
    A a = new B();
    System.out.println(a.f(3,5)); //代码1
    B b = (B)a;
    System.out.println(b.g(3,5));  //代码2
  }
}
